Composite doublers may be frequently used to repair both metallic and polymer-matrix composite aircraft structures. The doublers are bonded to the surface of the structure using one or more layers of a suitable adhesive. It is normally important to achieve a good bond between the doubler and the structure across the entire area of the doubler. However, in some cases, the surface of the structure may be uneven, and/or contain one or more depressions which create gaps between the doubler and the structure surface. In order to assure a complete bond having maximum strength, the gaps should be filled with adhesive. Accordingly, it is necessary to determine the size and location of the gaps between the doubler and the structure surface.
Existing techniques for measuring gaps between a structure surface and a doubler are time consuming, and measurement results may be depend upon the skill of the technician who makes the measurements and interprets the results. Moreover, the fact that the doubler is non-conductive and the structure surface is conductive limits the number of existing techniques that may be used for gap measurement.
Various devices are available for measuring gaps between two parts, but none is effective in rapidly mapping the gaps across the entire area of the doubler, particularly where the gaps are being measured between a conductive surface and a non-conductive surface. One known position sensing technology relies on the use of capacitive sensors. For example, capacitive blankets have been devised that are used as proximity sensors and boundary penetration sensors in security applications. These sensors detect the approach of intruders or the touching of a metal item or container that the sensors are intended to protect. Capacitive sensors have also been used to measure the gap between two conductive surfaces.
Accordingly, there is a need for a method and apparatus for rapidly mapping the gaps between a composite doubler, and a metal structural surface that is accurate, reliable and repeatable.